In a facility which treats radiation material, such as nuclear power plant or the like, in a case where an accident occurs, there is a possibility which flies (scatters) a radiation material having strong radioactivity over a wide range. Accordingly, it occurs to need to widely research whether the radiation material is present or not. Thus, a result of the research, if the radiation material is present, it is necessary to remove the radiation material.
Many human resources are necessary for a measurement whether radiation material is present or not. Accordingly, the worker having a little knowledge and skill may need to measure whether radiation material is present or not. In this case, some objects may occur as follows.
If radiation is detected in the radiation measurement apparatus, electric pulse is generated. The generated pulse is counted by a latter counting circuit. In a case where radioactivity is strong, the number of the radiation becomes large number. Since an interval between electric pulses narrows, the radiation measurement apparatus becomes a state (which will be hereinafter referred to as “pile-up”) where the electric pulses overlap each other.
If the pile-up is occurred in the radiation measurement apparatus, since a plurality of the pulses which overlaps each other are considered as single (one) pulse, in fact, a value (which will be hereinafter referred to as “count value”) counted by the counting circuit becomes smaller than actual radiation number detected by the radiation measurement apparatus. Further, in a case where the pile-up occurs by overlapping all electric pulses, the count value becomes zero (0). Thus, even though there is the radiation material having strong radioactivity in fact, there is a possibility being determined that here radioactivity is weak. In case of being determined that here radioactivity is weak, because the radiation material is not eliminated, a risk led to radiation exposure may be occurred.
Conventionally, a technique for detecting pile-up and a technique for preventing from pile-up are proposed (for example, refer to patent documents 1 and 2).
Further, if a count number of the counting circuit within measurement time exceeds over a measurement capacity of the counting circuit, because it occurs digit overflow (which will be hereinafter referred to as “overflow”), the count number output from the counting circuit becomes less than the count number input to the counting circuit. For example, in a case where an 8 bit counting circuit is used, maximum count value (measurement capacity) is 255. Accordingly, if the count value of the counting circuit reaches 256 within measurement time, the count value returns from 255 to 0. In above-described case, as same case as pile-up, it may be wrongly determined that a radioactivity is weak. Accordingly, the wrong determination is caused a risk led to radiation exposure.
Conventionally, for the sake of avoiding fault-measurement caused by the overflow, in the event that the counting circuit is overflowed, a technique for displaying contents that the counting circuit is overflowed is proposed (refer to non-patent document 1).